FR2701956A1 - Process for manufacturing flexible, solid, biodegradable films, and products obtained. - Google Patents

Abstract

The invention relates to a process for manufacturing flexible, solid, biodegradable films which can be used in particular for making wrappers or wrappers or for protecting surfaces or products. The method consists in using a plant material containing marrow such as sorghum, kenaf, sugar cane, corn cob, in extracting the hemicelluloses, in particular hemicelluloses B, in dissolving them, in spreading the solution on a surface in order to form a liquid layer and to perform drying of said layer in order to form the solid film. This is characterized by an internal hydration rate of between 10% and 25%, a water solubility greater than 200 g / l and a mechanical tensile strength of between 15 and 40 MPa.

Description

PROCESS FOR PRODUCING FLEXIBLE, SOLID FILMS,

BIODEGRADABLE, AND PRODUCTS OBTAINED

  The invention relates to a process for manufacturing flexible, solid, biodegradable films. It extends to the products obtained. By "film" is meant a layer with a controlled thickness that is less than the other dimensions; By "film-forming" is meant below the quality of a material capable of forming a flexible, solid film, having good mechanical strength (in particular rendering

  said film manipulated without risk of disintegration).

  Environmental constraints tend to limit the use of non-degradable packaging and to substitute for them products with a short decomposition cycle. It is currently known to make biodegradable films, that is to say naturally destructible films within short periods (less than one season) without

  leave polluting or toxic residues.

  A first type of process for producing biodegradable films intended for the manufacture of packaging consists in copolymerizing derivatives of polyhydroxylated acid (lactic acid, valeric acid); however, these processes are very expensive due to the nature of the raw material used and the cost of processing, which limits it.

applications considerably.

  In addition, a research avenue has recently been developed to try to manufacture biodegradable films from plant material extracts. In fact, these materials derived from annual plants are by nature biodegradable and are generally inexpensive. The following publications mention works on this subject: Aristippos Gennadios and Curtis L Weller, "Edible films

  and coating from wheat and corn proteins ", Food Tech.

  Oct 90, p 63-67; US Patent 4,843,655; Robert Coleman "Biodegradable plastics from potato waste double savings to environment" Agricult Eng Nov 90, p 20-22; Werner Wiedmann and Edgar Strobel, "Compounding of thermoplastic

  starch with twin-screw extruders "Starch 43 N '4 S p 138-

  These processes use either proteins, starch, or mixtures (gluten) which are extracted from plant materials (wheat, corn, potatoes) to form the base of the film; however, these materials do not by themselves have film-forming properties which make it possible to produce a film which is flexible and resistant: studies have shown that, used alone, they lead to a layer which hardens and becomes brittle. They add plasticizers to these raw materials (petroleum derivatives, glycerin) and subject the mixtures to thermomechanical treatments which develop combination reactions between plasticizer and base material, leading to a film-forming structural organization. The precise formulations protein and / or starch / plasticizer and the characteristics of the treatments depend on the authors and appear to provide films which have satisfactory qualities of flexibility and resistance; however, these methods are expensive because of the costs of plasticizers and the treatments required; moreover and above all, the film obtained is not completely biodegradable in the short cycle since it contains a more

hardly biodegradable.

  Thus, in these processes, the polysaccharides or proteins used until now have the sole function of forming the base of the film and have been simply chosen because of their biodegradable nature and their low cost: the plasticizing function which makes it possible to form a flexible and resistant film is provided by other means (addition of

third bodies and treatments).

  In addition, certain active products, in particular in the pharmaceutical field, are coated in biodegradable encapsulation films which are called to decompose in the organism to release the active principle; currently the material used to carry out these encapsulations is generally a gelatin of animal origin which is the only natural product available which combines the necessary properties: total biodegradability, absence of residual toxicity, film-forming character However, the mechanical strength of the films5 produced using gelatin is reduced and, if it makes it possible to produce packaging of the capsule type (small dimensions), it is totally insufficient for the manufacture of packaging or other packaging of

  In addition, sterilization of this type of product of animal origin is delicate and costly.

  The present invention proposes to provide a new process for manufacturing films capable in particular of allowing the production of packaging, packaging, or of ensuring the protection of surfaces or products. The objective of the invention is to manufacture flexible, solid films , biodegradable, benefiting from mechanical resistance properties suitable for carrying out both encapsulations and packaging,

  packaging or protection of larger area.

  Another objective of the invention is to allow this manufacture at a very reduced cost without

addition of plasticizer.

  The process according to the invention for manufacturing a flexible, solid, biodegradable film is characterized in that (a) a vegetable raw material containing marrow obtained from a marrow plant is used, (b) said vegetable raw material in the presence of a basic solution so as to dissolve the hemicelluloses, (c) separating the liquid phase from the solid phase, (d) treating said liquid phase so as to precipitate the hemicelluloses, (e ) extracting the crystallized precipitate obtained, (f) solubilizing said precipitate while hot, (g) spreading the solution obtained on a surface in order to form a liquid layer, and (h) drying said layer in order to form the

solid film.

  The invention is based on the demonstration of a remarkable and unknown property of hemicelluloses originating from the marrow of plants, namely that of forming a solid, flexible and resistant film, without additive or treatment after extraction. The process of the invention therefore makes it possible to produce a very inexpensive film, without additive; of course, for certain applications, it remains possible to add such and such an additive if necessary to increase the mechanical strength of the film or modify its properties, in particular certain

mechanical properties.

  It should be noted that, unexplained to date, plants with no marrow (wheat, barley) or the unpicked parts of other plants (external stem, stems of wood, straws) do not allow such a film: the gels formed from hemicellulosic extracts of these plants or parts of plants dehydrate while cracking and lead to a layer without

no clean clothes.

  The marrow alone can be used as the vegetable raw material after extraction from the plant and elimination of the external lignocellulosic fibers. In particular the marrow extracted from sorghum, kenaf, sugar cane or corn cobs, gives good results and leads to biodegradable films of very

good resistance.

  It is also possible to use whole stalks of sorghum, kenaf and sugar cane containing the marrow or whole corn stalks, excluding grains, containing the marrow Experiments have shown that less film-forming properties are obtained good than in the previous case, but perfectly satisfactory for leading to films of good resistance. It should be noted that the processes for extracting hemicelluloses from plants have already been the subject of numerous studies in order to optimize the parameters thereof. For example, the following publications describe methods for extracting and fractionating hemicelluloses of type A and B of annual plants: GR Woolard et al, "Note on the isolation of sorghum husk polysaccharides and fractionation of hemicellulose B", Am. Ass Cereal Ch 1976, p 601-608; R L Cunningham et al, "Hemicellulose isolation from annual plants", Biotech and bioengin Symp N O 17, 1986, p 159-168 However, these publications of general interest do not provide any

  particular instruction for making flexible films since they neither describe nor suggest the remarkable film-forming qualities of hemicelluloses originating from the plant marrow nor, a fortiori, the property which these have

  ci to form a film in the absence of any additive or

thermomechanical treatment.

  Preferably, the extraction of hemicelluloses is carried out in the process of the invention under the following conditions: the vegetable raw material is placed in the presence of a solution of soda or potassium hydroxide, with a weight concentration of between 1% and 10%, the vegetable raw material is mixed with the basic solution in a solid / liquid weight ratio at least equal to 0.04, the solution containing the vegetable material is heated, with stirring, to a temperature between 40 ° C. and 800 ° C. for a period understood

between 1/2 hour and 4 hours.

  Furthermore, the work of the inventors has shown that it was more particularly the type B hemicelluloses extracted from the marrow of the aforementioned plants which possessed very affirmed film-forming properties. It is possible to manufacture films using the mixture of hemicelluloses A and hemicelluloses B extracted; however, according to an advantageous embodiment of the process leading to increased cohesion and resistance films, type A hemicelluloses are first selectively precipitated and separated, the remaining liquid phase then being treated to precipitate hemicelluloses B which will serve only to form the film after separation and solubilization The hemicelluloses A which are thus separated have properties

  Theological which make them suitable for use as a technological or food additive (increase in the viscosity of a formulation); a fraction of these hemicelluloses A can, if necessary, be added to the film before drying to increase the viscosity.

  The selective precipitation of hemicelluloses A can be carried out by an acid addition up to a p H of between 5 and 7 while, after separation of these, the precipitation of hemicelluloses B will be carried out by adding alcohol to the liquid phase. quantity at least equal to 20 g of alcohol per gram of hemicellulose B contained in the solution Beforehand, it is advantageous to achieve a concentration of the liquid phase by evaporation so

  to remove between 30% and 60% of water.

  The crystallized hemicellulose precipitate can be dissolved hot in an aqueous medium at a temperature between 400 and 950 C, in a solid / liquid ratio at least equal to 100 g / l without reaching the

saturation of the medium.

  After spreading, the drying of the liquid layer is carried out by any conventional means: steaming at low temperature (30,500 ° C.), drying under a stream of hot air, natural drying. This drying removes the water from solubilization and leads to the formation of a flexible film having an internal hydration rate substantially between 10% and 25% (rate measured by "Mettler" infrared balance). The invention extends to flexible, solid, biodegradable films based on hemicellulose, produced by the process defined above; these films are characterized by: an internal hydration rate of between 10% and 25%, a water solubility greater than g / l, a mechanical tensile strength

  between 15 and 40 megapascal.

  The invention also extends to a film-forming product allowing the production of a flexible, solid, biodegradable film, characterized in that it is mainly constituted by hemicelluloses originating from sorghum marrow, kenaf, sugar cane or corn cobs. This film-forming product is obtained by carrying out the aforementioned hemicellulosic extraction, by drying the crystallized precipitate, then by conditioning it for transport. It will suffice for the film manufacturer to dissolve this product as defined above to produce the desired film. , given the simplicity of the operations of the process of the invention, the film manufacturer can also directly implement this process from plant materials containing marrow without going through the stage of drying and conditioning the crystallized precipitate obtained after the hemicellulosic extraction. The following examples illustrate the process of the invention and the characteristics of the films obtained.

EXAMPLE 1

  In this example, the vegetable raw material used is sorghum marrow alone, obtained by manual dismantling from fiber sorghum stalks

  (sorghum broom variety, two-color genus).

  The process used to extract hemicelluloses from this sorghum marrow involves an aqueous extraction * (temperature 600 C), then a

  soda extraction (temperature 600 C).

  g of sorghum marrow are mechanically ground (average particle size: 0.5 mm) and are introduced into a reactor containing 1.5 liters of water, with a view to carrying out a preliminary washing in order to remove the water-soluble impurities L The whole is kept under stirring at the temperature of 600 ° C. for one and a half hours. At the end of this preliminary washing step, filtration and rinsing with water are carried out. The marrow is then recovered and the filtrate discarded. The marrow thus washed is introduced into a reactor containing one liter of basic Na OH solution with a weight concentration equal to 4%. The whole is kept under stirring at a temperature of 60 ° C. for 90 minutes. At the end of this basic solubilization step of hemicelluloses, the solution is filtered on a filtering support; the filtrate is collected and the cake of lignocellulosic material is discarded The filtrate is then concentrated under reduced pressure (0.2 bar) with elimination of 50% water The concentrated solution is then acidified to a p H equal to 6 with acetic acid; the solution is left to stand for one hour. The hemicelluloses A which precipitate (4 g) are eliminated by filtration on a filtering support. The precipitation of hemicelluloses B contained in the filtrate is then carried out by addition of 95% ethanol at room temperature (one volume for one volume, ie 66 g of alcohol per gram of hemicellulose B precipitated) The crystallized precipitate of hemicellulose B is then filtered, washed with ethanol, then

air dried.

  9 g of a fine white powder are obtained, which has been characterized by elementary microanalysis, determination of uronic acids, mild acid hydrolysis and high performance liquid chromatography. These analyzes and the structural study led to a hemicellulose B structure of arabino-glucurono-xylanic type substituted with glucose, galactose and mannose residues; the main chain is xylanic and the main substituents are arabinose in 1-2 and

4-0-methylglucuronic in 1-3.

  To make a film from this powder, it is mixed with water at the rate of 1 gram of powder for 5 ml of water. The medium is heated with stirring until dissolved for 10 minutes at a temperature of 800 C After dissolution, the liquid is spread by natural pouring on a glass surface and dried in an oven at 40 C for two hours. A solid, flexible, transparent film is obtained, which can be handled dry without any particular precautions. film is characterized by: a thickness of 0.02 millimeter, an internal hydration rate of 17% ("Mettler" balance), a tensile strength of 37 M Pa, a water solubility greater than g / l. These characteristics make it possible to produce, with such a film, protective packaging for perishable foodstuffs, coating of seeds, protective layers of various surfaces (temporary protective layer) which are removed by simple washing with water.

  without generating polluting residues.

EXAMPLE 2

  This example is implemented in a manner analogous to Example 1, with the exception of the hemicellulose A filtration step which is omitted, in order to

  keep these hemicelluloses A in the solution.

  Acidification, addition of ethanol are carried out in

the same conditions.

  13 g of a fine, slightly gray powder are obtained, which has been characterized as above and which is a mixture of hemicelluloses B of Example 1 and hemicelluloses A, the structure of which is of analogous type, but with a degree of less substitution in

arabinose and uronic acid.

  The film obtained from this powder is transparent with a slight brown-gray coloration and is characterized by: a thickness of 0.04 millimeter, an internal hydradation rate of 20%, a mechanical tensile strength of 15 M Pa , a water solubility greater than g / i. This film can in particular be used to cover surfaces of products (pharmaceutical products) in order to condition them. EXAMPLE 3 This example is carried out in an identical manner to Example 1, but starting from a vegetable matter constituted by the whole stems of sorghum containing the marrow (20% by weight of marrow, 80% of

external fibers).

  In this example, 150 g of vegetable material were treated as in Example 1. 40 g of fine yellow / brown powder are obtained, which has been characterized as above. The difference with Example 1 lies in a higher proportion of arabinose and

of 4-0-methylgluronic.

  The film obtained is translucent and colored in brown. It is characterized by: a thickness of 0.03 millimeter, an internal hydration rate of 18%, a mechanical tensile strength of M Pa, a water solubility greater than

200 g / l.

EXAMPLE 4

  In this example, the vegetable raw material used is the whole corn cob, excluding grains. The process used to extract hemicelluloses from the cob, involves an extraction with soda (temperature: 60 C) 100 g of corn cobs are mechanically ground (average particle size: 1 mm) and are introduced into a reactor containing one liter of basic Na OH solution with a weight concentration equal to% The whole is kept under stirring at temperature. Acidification and addition of ethanol are 1 1

  carried out in a similar manner to Example 1.

  37.21 g of hemicellulose A are obtained and

  13.17 g hemicellulose B, in the form of a brown powder.

  The difference in treatment with Example 1 lies in the absence of a step of washing with water before the basic extraction. The film obtained from hemicelluloses B is transparent with a brown coloring and is characterized by: a thickness of 0.05 mm, an internal hydradation rate of 16%, a water solubility greater ag / l, a mechanical tensile strength of

31 M Pa.

EXAMPLE 5

  In this example, the vegetable raw material used is the kenaf marrow alone, obtained by

  mechanical dismantling of kenaf stems.

  The implementation protocol is the same as in Example 1 It results in an uncolored transparent film characterized by: a thickness of 0.04 mm, an internal hydradation rate of 18%, and a solubility at l 'water

more than 200 g / l.

  The mechanical tensile strength was lower than in the previous examples, but sufficient to allow the use of this film as a protector for solid surfaces, for example coating of seeds. It should be noted that the implementation parameters of this example have not been optimized for

  obtaining a film of good mechanical strength.

Claims (9)

  1 / Process for manufacturing a flexible, solid, biodegradable film, in particular film for conditioning, packaging or surface or product protection, characterized in that (a) a vegetable raw material containing marrow obtained from is used of a marrow plant, (b) putting said vegetable raw material in the presence of a basic solution so as to dissolve the hemicelluloses, (c) separating the liquid phase from the solid phase, (d) treating said liquid phase so as to precipitate the hemicelluloses, (e) extracting the crystallized precipitate obtained, (f) solubilizing said precipitate while hot, (g) spreading the solution obtained on a surface in order to form a liquid layer, and ( h) drying said layer in order to form the solid film.   2 / A method according to claim 1, characterized in that (a) is used as vegetable raw material marrow extracted from sorghum, kenaf, cane sugar or corn cobs, with elimination of   external lignocellulosic fibers.   3 / A method according to claim 1, characterized in that (a) is used as vegetable raw material, the whole stalks of sorghum, kenaf, cane sugar containing the marrow or the whole cobs   corn, excluding grains, containing the marrow.   4 / Method according to one of claims   1, 2 or 3, in which (b) the vegetable raw material is placed in the presence of a solution of soda or potash,   weight concentration between 1% and 10%.   / Method according to claim 4, in which (b) the vegetable raw material is mixed with the basic solution in a solid / liquid weight ratio to less than 0.04.   6 / Method according to one of claims   4 or 5, in which (b) the solution containing the plant material is heated, with stirring, to a temperature of between 40 ° C. and 800 ° C. for a period of time included between 1/2 hour and 4 hours.   7 / Method according to one of claims   1 to 6, characterized in that (d) the liquid phase is treated: (d 1) by selectively precipitating type A hemicelluloses, (d 2) by separating these hemicelluloses A from the liquid phase, then (d 3) by rushing them   type B hemicelluloses of the liquid phase, with a view to extracting only these.   8 / A method according to claim 7, in which: (d 1) the hemicelluloses A are precipitated selectively by the addition of acid up to a p H of between 5 and 7, (d 2) the precipitate is eliminated, then ( d 3) an alcohol is added to the liquid phase in an amount at least equal to 20 g of alcohol per gram of hemicellulose B contained in the solution, in order to precipitate said hemicelluloses B. 9 / A method according to claim 8, in which (d O) a prior concentration of the liquid phase is carried out by evaporation so as to eliminate between 30% and 60% water. / Method according to one of   claims 1 to 9, in which (f) the   precipitate crystallized in an aqueous medium brought to a temperature between 40 and 95 C, in a solid / liquid ratio at least equal to 100 g / l without reaching the saturation of the medium.   11 / Flexible, solid, biodegradable film, based on hemicellulose, produced by implementing the process   according to one of claims 1 to 10, characterized   by: an internal hydration rate of between 10% and 25%, a water solubility greater than g / l,   a mechanical tensile strength of between 15 and 40 M Pa.   12 / Film-forming product allowing the production of a flexible, solid, biodegradable film, characterized in that it is mainly constituted by hemicelluloses obtained from sorghum marrow, kenaf, cane sugar or corn cobs. 13 / A method of manufacturing a film-forming product according to claim 12, characterized in that it comprises the following steps: (a) using a vegetable raw material based on sorghum, kenaf, sugar cane or corn cobs containing marrow, (b) putting said vegetable raw material in the presence of a basic solution so as to dissolve the hemicelluloses, (c) separating the liquid phase from the solid phase, (d) treating said phase liquid so as to precipitate the hemicelluloses, (e) extracting the crystallized precipitate obtained, then drying said precipitate and conditioning it for transportation.